1. Field of the Invention
The present invention relates generally to brake testers and more specifically to a tester for pneumatic brakes for measuring the elapsed time between the actuation of the brake pedal and the attainment of a predetermined pressure with the brake chamber.
2. Description of the Prior Art
On May 17, 1974, the Federal Government issued certain regulations, which regulations may be found in 39. F. R. 17550, assigning minimum required standards for pneumatic brake systems. More specifically, the above named Federal Regulations specify two tests for pneumatic brake systems. The first test, denoted the brake actuation
"With an initial service reservoir system air pressure of psi, the air pressure in each brake shall in the case of trucks and buses, reach 60 psi in not more than 0.35 seconds measured from the first movement of the service brake control and, in the case of trailers reach 60 psi in not more than 0.25 seconds measured from the first moment the service brake control". The second test, denoted the brake release time test provides in part: PA1 "With an initial brake chamber air pressure of 95 psi, the air pressure in each brake chamber shall, in the case of trucks and buses, fall to 5 psi in not more than 0.50 seconds measured from the first movement of the service brake control and, in the case of trailers, fall to 5 psi in not more than 0.60 seconds measured from the first movement of the brake control".
Following the promulgation of the above regulations, which became effective on Jan. 1, 1975, and Mar. 1, 1975 respectively, several brake testers were developed to measure the brake actuation and release time as required by the regulations. These previously known brake testers typically comprise a test unit situated externally of the vehicle. A pressure transducer attached to the brake chamber provides the required pressure input signals to the brake tester while a second line connected to the brake pedal provides a signal upon the movement of the brake pedal. These previously known brake testers essentially comprise only the timing circuit which begins to run upon actuation of the brake pedal and which is stopped by the attainment of a predetermined pressure condition within the brake chamber.
These previously known brake testers suffer from many advantages unknown to the present invention. First, two operators are required to run the test operation, namely, one person in the vehicle to actuate the brake pedal and the other person at the brake tester to record the results of the test. Needless to say, the requirement of two persons for each testing operation greatly increases the labor costs of the brake testing operation and is therefore undesirable.
Second, the previously known brake testers are typically designed with preset pressure controls so that only a single test, i.e. the brake application test or the brake release test, may be performed at any given time. Thus it has become the practice of the previously known brake testers to conduct the brake actuation test on the multiple brake chambers and thereafter reset the pressure controls and conduct the brake release test. This procedure, required by the previously known brake testers, necessitates the running of essentially two independent tests on each brake cylinder and therefore increases the time required for a complete test of the brake cylinder.
Still another problem in the previously known brake testers is such that such testers utilize the vehicle air compressor to pressurized the air reservoir. It is very difficult however to obtain the precise pressure of 95 psi, needed for the initiation of the brake release test, or 100 psi, needed for the initiaton of the brake application test, within the vehicle reservoir by using the vehicle air compressor. It has been found that much time is wasted by the test operators in adjusting the air pressure in the vehicle air reservoir due to 95 psi or 100 psi as required by the Federal Regulation and again this is undesirable.